[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [xen master] xen: Fix latent check-endbr.sh bug with 32bit build environments
commit 0af91dc0326cba12795e0b8fa8f665776e2a9e13 Author: Andrew Cooper <andrew.cooper3@xxxxxxxxxx> AuthorDate: Fri Jul 15 12:53:09 2022 +0100 Commit: Andrew Cooper <andrew.cooper3@xxxxxxxxxx> CommitDate: Mon Jul 18 15:32:27 2022 +0100 xen: Fix latent check-endbr.sh bug with 32bit build environments While Xen's current VMA means it works, the mawk fix (i.e. using $((0xN)) in the shell) isn't portable in 32bit shells. See the code comment for the fix. The fix found a second latent bug. Recombining $vma_hi/lo should have used printf "%s%08x" and only worked previously because $vma_lo had bits set in it's top nibble. Combining with the main fix, %08x becomes %07x. Fixes: b2ebe879a444 ("xen: Fix check-endbr.sh with mawk") Reported-by: Jan Beulich <JBeulich@xxxxxxxx> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx> --- xen/tools/check-endbr.sh | 25 +++++++++++++++++++++---- 1 file changed, 21 insertions(+), 4 deletions(-) diff --git a/xen/tools/check-endbr.sh b/xen/tools/check-endbr.sh index b3febd6a4c..b97684ac25 100755 --- a/xen/tools/check-endbr.sh +++ b/xen/tools/check-endbr.sh @@ -61,19 +61,36 @@ ${OBJDUMP} -j .text $1 -d -w | grep ' endbr64 *$' | cut -f 1 -d ':' > $VALID & # the lower bits, rounding integers to the nearest 4k. # # Instead, use the fact that Xen's .text is within a 1G aligned region, and -# split the VMA in half so AWK's numeric addition is only working on 32 bit -# numbers, which don't lose precision. +# split the VMA so AWK's numeric addition is only working on <32 bit +# numbers, which don't lose precision. (See point 5) # # 4) MAWK doesn't support plain hex constants (an optional part of the POSIX # spec), and GAWK and MAWK can't agree on how to work with hex constants in # a string. Use the shell to convert $vma_lo to decimal before passing to # AWK. # +# 5) Point 4 isn't fully portable. POSIX only requires that $((0xN)) be +# evaluated as long, which in 32bit shells turns negative if bit 31 of the +# VMA is set. AWK then interprets this negative number as a double before +# adding the offsets from the binary grep. +# +# Instead of doing an 8/8 split with vma_hi/lo, do a 9/7 split. +# +# The consequence of this is that for all offsets, $vma_lo + offset needs +# to be less that 256M (i.e. 7 nibbles) so as to be successfully recombined +# with the 9 nibbles of $vma_hi. This is fine; .text is at the start of a +# 1G aligned region, and Xen is far far smaller than 256M, but leave safety +# check nevertheless. +# eval $(${OBJDUMP} -j .text $1 -h | - $AWK '$2 == ".text" {printf "vma_hi=%s\nvma_lo=%s\n", substr($4, 1, 8), substr($4, 9, 16)}') + $AWK '$2 == ".text" {printf "vma_hi=%s\nvma_lo=%s\n", substr($4, 1, 9), substr($4, 10, 16)}') ${OBJCOPY} -j .text $1 -O binary $TEXT_BIN +bin_sz=$(stat -c '%s' $TEXT_BIN) +[ "$bin_sz" -ge $(((1 << 28) - $vma_lo)) ] && + { echo "$MSG_PFX Error: .text offsets must not exceed 256M" >&2; exit 1; } + # instruction: hex: oct: # endbr64 f3 0f 1e fa 363 017 036 372 # endbr32 f3 0f 1e fb 363 017 036 373 @@ -84,7 +101,7 @@ then else grep -aob -e "$(printf '\363\17\36\372')" -e "$(printf '\363\17\36\373')" \ -e "$(printf '\146\17\37\1')" $TEXT_BIN -fi | $AWK -F':' '{printf "%s%x\n", "'$vma_hi'", int('$((0x$vma_lo))') + $1}' > $ALL +fi | $AWK -F':' '{printf "%s%07x\n", "'$vma_hi'", int('$((0x$vma_lo))') + $1}' > $ALL # Wait for $VALID to become complete wait -- generated by git-patchbot for /home/xen/git/xen.git#master
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